Gas turbine with extended turbine blade stream adhesion

ABSTRACT

A gas turbine may include turbine blades configured to improve stream adhesion by selectively attracting or reducing repulsion of charged particles carried by a combustion gas stream.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit from U.S. ProvisionalPatent Application No. 61/582,243, entitled “GAS TURBINE WITH EXTENDEDTURBINE BLADE STREAM ADHESION”, filed Dec. 30, 2011, which, to theextent not inconsistent with the disclosure herein, is incorporated byreference.

The present application is related to U.S. Non-Provisional patentapplication Ser. No. 13/172,652, entitled “GAS TURBINE WITH COULOMBICTHERMAL PROTECTION”, filed Dec. 12, 2012, which, to the extent notinconsistent with the disclosure herein, is incorporated by reference.

BACKGROUND

Gas turbines, which (for example) are used in terrestrial powergeneration and jet aircraft propulsion, include turbine blades that aredesign-constrained according to a maximum “lift” or rotational forcethat may be applied by any one blade under a given set of conditions.One limiting factor is a tendency for streamwise pressure variationalong a low pressure side of the turbine blade to cause a near-surfacevelocity reversal with concomitant loss of stream adhesion to theturbine blade. The phenomenon of loss of adhesion may typically bereferred to as flow separation. Flow separation may be regarded as aform of aerodynamic stall. The tendency to undergo flow separation maybe most pronounced near trailing edges of the turbine blades.

According to a related application, gas turbine blades may be configuredto operate at higher than previously attainable combustion gas (freestream) temperatures through the use of Coulombic repulsion of chargedparticles in the combustion gas, combined with film-cooling. This mayresult in higher thermodynamic efficiency of the gas turbine. However, ahigher free stream temperature may result in higher lift per turbineblade at relatively lower free stream velocity. This greater lift atlower velocity may increase streamwise pressure variations along the lowpressure side of the turbine blade, and hence (absent redesign ofturbine blade aerodynamics) may be associated with an increasedpropensity for flow separation.

Moreover, the Coulombic repulsion itself may tend to urge the freestream away from surfaces of the turbine blade, and further add to flowseparation, especially on the low pressure side of the turbine blade.

Additionally, the power output range (dynamic range) of a gas turbinemay be related to an allowable range of combustion gas volume deliveredto the turbine at a given rotational rate of the rotor, which (for agiven cross-sectional area) can be related to a range of mass flows atwhich a given turbine blade/stator aerodynamic design will work mostefficiently. Just as an airplane wing will stall at low velocities,corresponding to a high angle of attack, and operate less efficiently atvelocities that differ significantly from a designated cruise velocity,turbine blades may suffer similar flow separation at extremes of dynamicrange.

Moreover, flow separation effects may force gas turbines to use arelatively large number of stages to extract all power. More stagesnegatively affect capital cost, weight, and size of the gas turbine(particularly the length of the rotor shaft).

What is needed is a gas turbine that can operate with a highercombustion gas temperature without requiring turbine blade redesign, canexhibit larger dynamic range, have a lower capital cost, have a lowerweight, and/or have a reduced size compared to previous gas turbines.

SUMMARY

According to an embodiment, a gas turbine may include a combustorconfigured to output a combustion gas stream, the combustion gas streambeing controlled or driven to at least intermittently or periodicallyinclude charged particles having a first sign. For example the firstsign may be positive during at least an instant. The gas turbine alsoincludes at least one turbine configured to receive the combustion gasstream (carrying the charged particles at least intermittently orperiodically). The turbine includes at least one turbine stage havingturbine blades. Each turbine blade includes a repelling surfaceconfigured to be at least intermittently or periodically held or drivento a repelling voltage having a polarity the same as the chargedparticles having the first sign. At least some turbine blades alsoinclude an adhesion surface configured to be at least intermittently orperiodically held, driven, or in equilibrium to an adhesion voltage orcharge having lower magnitude than or opposite polarity from therepelling voltage. This may cause a reduced net force of repulsion, thereduction of which may improve boundary layer and free stream adhesion.FIG. 3A shows an example.

An air channel may be configured to deliver film-cooling air adjacent tothe repelling surface of the turbine blade.

According to another embodiment, a method of operating a gas turbineincludes providing a combustion gas stream at least intermittently orperiodically carrying charged particles having a first sign; convertingthermodynamic energy to rotational energy with turbine blades; at leastintermittently or periodically applying Coulombic repulsion to thecharged particles from a repelling portion of each turbine blade byapplying a repelling voltage to the repelling portion; and at leastintermittently or periodically applying reduced Coulombic repulsion fromor increased Coulombic attraction to an adhesion portion of each turbineblade by at least one of shielding the Coulombic repulsion caused by therepelling voltage or by applying an adhesion voltage to attract thecharged particles to the adhesion portion of the turbine blade.

The method may include providing film-cooling air adjacent to at leastthe repelling portion of the turbine blade.

According to an embodiment, a turbine blade includes a repelling surfaceconfigured to be at least intermittently or periodically held or drivento a repelling voltage and an adhesion surface configured to be at leastintermittently or periodically held, driven, or in equilibrium to anadhesion voltage or charge having lower magnitude than or oppositepolarity from the repelling voltage. The turbine blade may include a gaschannel configured to deliver film-cooling gas adjacent to at least therepelling surface. The adhesion surface may include an electricalinsulator disposed adjacent to the repelling surface and an electricalconductor or semiconductor disposed adjacent to the electricalinsulator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a gas turbine, according to an embodiment.

FIG. 2 is a diagram illustrating cascaded momentum transfer fromCoulombically repelled particles to neutral particles, according to anembodiment.

FIG. 3A is a streamwise sectional diagram of a turbine blade configuredfor extended free stream adhesion, according to an embodiment.

FIG. 3B is a diagram showing fluid velocities and free stream adhesionover the turbine blade of FIG. 3A, according to an embodiment.

FIG. 4 is a diagram from an A-A view illustrated on FIG. 3A including anadhesion surface having a spanwise varying adhesion surface couplingefficiency, charge/voltage, or area, according to an embodiment.

FIG. 5 is a span-wise B-B view of portions of a repelling surface and anadhesion surface of the turbine blade of FIGS. 3A and 4, according to anembodiment.

FIG. 6 is a span-wise B-B view diagram of portions of a repellingsurface and an adhesion surface of the turbine blade of FIGS. 3A and 4,according to another embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here.

FIG. 1 is a block diagram of a gas turbine 101, according to anembodiment. The gas turbine 101 includes a compressor 112 configured tocompress air, the compressed air then entering a combustor 114. Fuel isburned in the combustor 114 to raise the temperature of the air andproduce combustion products. The hot combustion products exit thecombustor 114 and travel through a turbine 116. The turbine 116 includesturbine blades attached to a shaft 118. The combustion gases impingingon the turbine blades cause rotation of the shaft 118, which providespower to the compressor 112. The shaft 118 may also be coupled to fanblades (such as in an aircraft jet engine, not shown) or an electricalpower generator or alternator (such as in a terrestrial power generatoror aircraft auxiliary power unit (APU), not shown).

Fuel is introduced to the combustor 114 through one or more nozzles 120.The combustor 114 includes a wall 122 that must be kept cool. Typically,the wall 122 may be cooled by introducing cool air through vents (notshown). The combustor wall 122 may also be cooled according to methodsdescribed herein.

Turbine blade cooling air from the compressor may be admitted, such asthrough an air passage 124 formed by the shaft 118. The turbine bladecooling air provides cooling to the shaft 118 by forced convection, andtravels into the turbine blades. Cooling of the turbine blades isdescribed in greater detail in conjunction with FIGS. 2 and 3A.According to an embodiment, one or more electrode(s) 126 may be disposednear the fuel nozzle(s) 120. Optionally, the one or more electrode(s)126 may be coextensive with at least a portion of the fuel nozzle(s)120. The electrode(s) 126 may apply a continuous or modulated voltagepotential near flame(s) anchored by the fuel nozzle(s) 120.

During combustion, a flame produces charged intermediate species ortransition states. These charged species include free electrons, fueland fuel fragments, oxygen radicals, etc. Conservation of chargedictates that positive and negative charges nominally balance such thatthe total charge is approximately neutral. The electrode(s) 126 mayattract charge of opposite sign. For example, the electrode(s) 126 maybe held or modulated to a positive voltage, and may responsively attractelectrons from the flame. Similarly, the electrode(s) 126 may be held ormodulated to a negative voltage, which responsively removes positivelycharges species from the flame. The electrode(s) 126 may be modulatedacross a positive and negative voltage range, may be modulated involtage above and below a DC bias voltage, and/or may be held at asubstantially constant DC bias voltage. According to embodiments, theelectrode(s) 126 may be modulated between relative ground and a positivevoltage of a few hundred volts at a time-varying frequency of a fewkilohertz up to a few hundred kilohertz. Higher or lower voltages may beused and/or higher or lower frequency may be used.

The effect of at least intermittently or periodically removing chargedparticles of one sign or polarity from the flame results in a chargeimbalance that may be used to apply Coulombic forces on the combustiongas. The applied Coulombic forces may directly affect the movement ofcharged particles, and the charged particles, in turn, may transfermomentum to uncharged particles. As used herein, a “particle” mayinclude an aerosol such as unburned fuel, a gas molecule, an ion, and/oran electron, for example. As will be described below, the appliedCoulombic forces may be used to repel hot gas from temperature-sensitivesurfaces, such as turbine blades, turbine inlet guide vanes, turbinestators, the turbine shaft, and/or the combustor wall.

The electrode(s) 126 may be voltage isolated from other portions of thegas turbine 101 by suitable clearances (e.g., “air gaps”) or electricalinsulators 128. A voltage source 134 may provide the voltage to theelectrode(s) 126. The voltage source 134 may also apply a voltage to thecombustor wall 122 and to the turbine 116 blades and optionally turbineshaft 118 via a voltage conduction circuit 130. The voltage conductioncircuit 130 may include one or more electrical insulators 128.Optionally, the voltage source 134 may provide different voltages to theelectrode(s) 126, combustor wall 122, and/or turbine 116 blades. Thevoltage source 134 may include a DC voltage source and/or a modulatedvoltage source.

Optionally, the number density of ions may be increased or the ions maybe produced by a mechanism other than the electrode(s) 126 acting on thecombustion reaction to produce a majority species. Increasing the numberdensity of ions may be used to increase the Coulombic forces acting onthe hot gas. Operating by a mechanism other than the electrode(s) 126acting on the combustion reaction to produce a majority species may beused according to designer preferences.

According to an embodiment, an electrode (optionally, electrode(s) 126or a different electrode, not shown) may be operated at sufficientvoltage to generate a corona discharge upstream of the turbine blades.In another embodiment, an additive such as one or more alkali salt(s)may be included in the fuel. In another embodiment, an additive such asone or more alkali salt(s) may be injected into the combustor 114.

Approaches for producing or increasing an ion number density aredescribed by Lawton and Weinberg in Electrical Aspects of Combustion,incorporated herein by reference.

It is possible that alternative theories could be constructed to explainthe conversion of Coulombic repulsion to electrostatic or electrodynamicacceleration of the bulk region of the fluid. FIG. 2 is a diagram 201illustrating cascaded momentum transfer from electrostatically-repelledparticles to neutral particles, according to an embodiment. Throughoutthe description herein, it may be assumed that voltages are either toolow to cause dielectric breakdown (arcing) or that passive or activevoltage control will decrease voltages under conditions where dielectricbreakdown or incipient dielectric breakdown occurs. While voltages andparticle charges are shown as positive in FIG. 2, the same effect may beseen with negative voltages and negative particle charges (or, as willbe described more fully below, sign-modulated similar charges).Accordingly, the principles illustrated by FIG. 2 may be applied to asystem using one or more constant or modulated positive voltages, one ormore constant or modulated negative voltages, or positive and negativevoltages modulated in time. In most gas turbine systems, it may beassumed that each particle corresponds to a gaseous molecule, atom, orion.

A body, such as a turbine blade 202, may be driven to or held at avoltage, V_(T), such as a positive voltage. A film-cooling layer 204 mayinclude substantially only neutral particles 206. Neutral particles 206may be regarded as not interacting with the positive voltage V_(T) ofthe body 202 (ignoring dipole interactions). Accordingly, thefilm-cooling layer 204 may be substantially unaffected by Coulombicforces.

A bulk region 207, separated from the body 202 by the film-cooling layer204, may include neutral particles 206 and charged particles 208. Forpurposes of description, charged particles 208 may be regarded aspositively charged. The positively charged particles 208, 208 a may beCoulombically (electrostatically) repelled by the same sign voltageV_(T) of the body 202 and may be responsively accelerated along a path209. The path 209 may be visualized as the positive particle 208“falling” through a voltage gradient caused by the voltage V_(T) of thebody 202. The path 209 (e.g., the mean free path 209) typically has aprobable distance inversely proportional to density. The path 209eventually intersects another particle 206, whereupon a collision 210between the charged particle 208 and a second particle 206 causesmomentum transfer from the charged particle 208 to the second particle206. For an average elastic collision (or a particular elastic collisionof favorable orientation), momentum of the charged particle 208 may behalved, and the momentum of the second particle 206 may be increased bythe same amount.

For systems where charged particles 208 are present in low concentration(which corresponds to most or all embodiments described herein), mostcollisions 210 involving a charged particle 208 may be binaryinteractions between the charged particle 208 and a neutral particle206. After the collision 210, momentum transferred to the neutralparticle 206 causes it to travel a distance near a mean free path untilit undergoes a collision 212 with another particle after a timeapproximating a mean time between collisions. For systems where chargedparticles 208 are present in low concentration, most collisions 212involving momentum transfer from a neutral particle 206 may be binaryinteractions between the first neutral particle 206 and a second neutralparticle 206′. For an average elastic collision, half the momentum ofthe first neutral particle 206 may be transferred to the second neutralparticle 206′. The first neutral particle 206 and the second neutralparticle 206′ may then travel along respective paths until each collideswith other respective neutral particles in collisions 212 and momentumis again transferred. The series of neutral particle collisions 212 thusdistribute momentum originally received from the charged particle 208across a large number of neutral particles 206 according to anexponential 2^(N) progression in a parallel process.

Meanwhile, the charged particle 208 is again accelerated responsive toCoulombic interaction with the voltage V_(T) of the body 202, andaccelerates along a path to another collision 210, whereupon the processis repeated as described above.

According to an illustrative embodiment, charged particles 208 may bepresent in the free stream (also referred to as a combustion gas stream)207 at a concentration on the order of one to one-hundred parts perbillion (ppb). According to the geometric momentum distributiondescribed above, momentum may be transferred from one charged particle208 to a majority of all particles 206, 208 in the free stream 207 inabout 24 to 30 generations of collisions 210, 212 (2³⁰>1×10⁹,2²³>8×10⁶). The amount of transferred momentum at each collision is afunction of the voltage V_(T) of the body 202, the magnitude of chargecarried by the charged particle 208, the density of the free stream 207(and hence the mean free path length), and the distance from the surfaceof the body 202 to the charged particle 208 at the point of eachcollision 210.

Because Coulombic forces substantially do not act on particles in thefilm-cooling layer 204, the film-cooling layer 204 undergoessubstantially no repulsion. Moreover, the Coulombic repulsion acting onthe charge-carrying free stream 207 may be viewed as producing a partialvacuum in regions between the surface of the charged body 202 and thefree stream 207. The film-cooling layer 204 may thus also be viewed asbeing held in contact with the surface of the body 202 by the partialvacuum produced by evacuation of charged particles 208.

Referring to FIG. 1, an optional adhesion voltage lead 136 may providean adhesion voltage to an adhesion surface of the turbine blades. Theadhesion voltage will be explained more fully in conjunction with FIGS.3A, 4, 5, and 6.

An optional counter-ion injection lead 138 may optionally provide chargeof opposite sign to the charge imbalance in the gas stream, and thusallow the combustion reaction to proceed to completion. Optionally, thecounter-ion injection lead 138 may be configured to inject thecounter-ions after the first stage turbine blades, between later turbinestages, or at the outlet end of the turbine 116. The counter-ioninjection lead may produce exhaust gas that is less reactive than acharged gas stream, thereby reducing environmental effects of the systemdescribed herein. The counter-ion injection lead may further be used tobalance charges delivered by the voltage source 134, and thereby reducepower consumption and/or charge bleed to isolated system components.

FIG. 3A is a streamwise sectional diagram of a region 301 including aturbine blade 302 configured for Coulombic thermal protection from hotcombustion gases, and extended free stream adhesion of the gases to thesurface of the turbine blade 302, according to an embodiment. Asdescribed above, a combustion gas stream 207 may at least intermittentlyor periodically include charged particles 208. The turbine blade 302 mayinclude a repelling surface 304 configured to be at least intermittentlyor periodically held or driven to a repelling voltage V_(T). Therepelling voltage V_(T) may typically be driven to a voltage having thesame sign as a majority of charged particles 208 proximate to theturbine blade 302 such that repulsion of the hot combustion gas stream207 occurs according to a mechanism similar to that described inconjunction with FIG. 2, or according to another mechanism.

A gas channel 306 may be configured to deliver film-cooling gas 204adjacent to at least the repelling surface 304. For example, the gaschannel 306 may be a first gas channel configured to deliverfilm-cooling gas through slots or holes 308 proximate a flow forwardedge 310 of the repelling surface 304. Nominally, the film-cooling gas204 and the combustion gas stream 207 may travel along streamlines 312parallel to the surface 304 of the turbine blade 302. Because streamingis parallel to the surface 304, the film-cooling gas 204 and thecombustion gas 207 may tend to not mix. Moreover, the repulsion of thecharged particles 208 by the repelling voltage V_(T) of the repellingsurface 304 may tend to prevent mixing of the combustion gas 207 withthe film-cooling gas 204.

A location 314 along the surface 304 may be characterized by a firstpressure P₁, as shown in FIG. 3A. FIG. 3B is a diagram showing fluidvelocities and possible flow separation over the turbine blade of FIG.3A, according to an embodiment. Referring to FIG. 3B, fluid velocitynear the surface 304 at the location 314 corresponding to the firstpressure P₁ may follow a function represented by the velocity curve 316.The velocity curve 316 conforms to a requirement that velocity v be zeroat the surface 304. Velocity v represented by the velocity curve 316 ispositive at all points not at the surface 304 and asymptoticallyapproaches the free stream velocity v_(F) at locations removed from thesurface 304.

Referring to FIG. 3A, for a lifting body such as the turbine blade 302,the gas pressure over the low pressure surface (top surface) of theturbine blade 302 may increase with distance along the surface 304 suchthat a second pressure P₂ at a second point 318 on the low pressuresurface is higher than the first pressure P₁ at the first point 314nearer the flow forward edge 310 of the turbine blade 302. In otherwords, P₁<P₂.

The system illustrated by FIGS. 3A and 3B may be represented accordingto the Navier-Stokes partial differential residual:

v∂v/∂s=(−1/ρ)∂p/∂s+u∂ ² v/∂y ²

where s is the streamwise axis,

y is the normal axis,

v is velocity along the streamwise axis,

ρ is density,

p is pressure, and

u is a second derivative constant.

For a case where non-streamwise velocity gradients and gradientcurvatures are small compared to streamwise gradients, the equationreduces to:

v∂v/∂s=(−1/ρ)∂p/∂s.

In other words, the change in streamwise velocity is nonlinear andnegative with the increase in pressure along the stream path. Forotherwise conventional turbine blade designs (e.g. absent “steps”),pressure may vary monotonically and increasing with distance along theturbine blade 302 beyond the minimum pressure point.

When ∂p/∂s>0,

velocity v decreases as s increases.

There may be conditions under which v is less than or equal to 0, aresult of which is illustratively shown in FIGS. 3A and 3B. Thiscorresponds to a flow separated velocity profile illustrated by a v<0solution shown as the velocity curve 322 in FIG. 3B. For steady y-axisconditions, the velocity inversion in the velocity profile 322 maycorrespond to spanwise vortex shedding.

For cases where P₂ is sufficiently greater than P₁, the streamline 312may lift off the surface 304 of the turbine blade 302 as indicated by astall streamline 320. In fact, the streamline 320 may represent theouter edge of a region characterized by the spanwise vortex shedding.Such behavior may be referred to as an aerodynamic stall.

Referring again to FIG. 3B, aerodynamic stall may occur when a velocityprofile 322 includes a portion near the surface 304 having a negativevalue. As shown, the velocity profile 322 represents a flow directionreversal at a small distance from the surface 304 up to a magnitude of−v_(MAX). For comparison, a nominal velocity profile 316 at the location314 is superimposed.

Referring again to FIG. 3A, according to embodiments, the turbine blade302 includes an adhesion surface 324 configured to prevent the lift-offor stall behavior 320, and instead substantially keep the flow 312 incontact with the upper surface of the turbine blade 302, as illustratedby the streamline 326. Referring to FIG. 3B, the adhesion surface 324may act to create a velocity profile 328. The velocity profile 328 is“squished” such that velocity increases faster near the surface suchthat a measurable negative velocity is substantially avoided, and stalldoes not occur.

The adhesion surface 324 creates the velocity profile 328 and thestreamline 326 by reducing or reversing the repulsion exerted by therepelling surface 304 across at least a portion of the turbine blade302. The adhesion surface 324 is configured to be at leastintermittently or periodically held, driven, or in equilibrium toproduce an adhesion voltage V_(A) or charge having lower magnitude thanor opposite polarity from the repelling voltage V_(T).

As described above, the repelling surface 304 may be configured to repelthe combustion gas stream 207 by Coulombic repulsion. The gas channel308 may thus deliver the film-cooling gas 204 to a volume adjacent tothe repelling surface 304 between the repelling surface 304 and thecombustion gas stream 207. The Coulombic repulsion of the combustion gasstream 207 by the repelling surface 304 may help to maintain therelative positions of the repelling surface 304, the film-cooling gas204, and the combustion gas 207, and thereby reduce turbine blade 302heating and deterioration or failure.

According to embodiments, the adhesion surface 324 may act to shield thecombustion gas 207 from the repelling action of the repelling surface304 at locations prone to stall 318.

According to embodiments, the adhesion surface 324 may be configured asan electrical shield to shield the combustion gas stream 207 from therepelling voltage V_(T) applied to the repelling surface 304 of theturbine blade 302. The adhesion surface 324 may provide extended flowadhesion and reduce or substantially eliminate flow separation, as shownby the alternative, non-separated stream 326 and the “squished” velocityprofile 328.

An electric field environment different than the electric fieldenvironment caused by V_(T) may be formed by the adhesion surface 324.For example, a conductor or semiconductor of the adhesion surface 324(optionally as image charge balanced against charges deposited on anoverlying insulator) may be driven or otherwise carry an equilibrium orpseudo-equilibrium voltage or charge deposited by the ionized combustiongas 207. For example, the charge or voltage V_(A) carried by theadhesion surface may be normally in equilibrium with the time-averagedcharge(s) carried by the combustion gas. According to one view, this maybe visualized as a Faraday cage shielding the electric field environmentcorresponding to adhesion flow 326. A charge 208 b shielded from therepulsion voltage V_(T) and/or responsive to an adhesion voltage V_(A)may “feel” less Coulombic acceleration away from the surface 304 thanthe acceleration felt by charges 208 a operatively coupled to therepulsion voltage V_(T).

According to an embodiment, the adhesion surface 324 may be configuredto be in charge equilibrium or pseudo-equilibrium with the chargedcombustion gas stream 207 such that the adhesion surface 324 is chargedto an adhesion voltage V_(A) having an average value lower in magnitudethan an average of the turbine blade 302 repelling voltage V_(T). Forexample, at least one of the sign of the charged particles 208 or theconcentration of the charged particles 208 in the combustion gas 207 maybe modulated responsive to modulation of voltage of the electrode(s) bythe voltage source (FIG. 1, 126, 134) according to a desired equilibriumor pseudo-equilibrium voltage.

According to other embodiments, the adhesion surface 324 may be drivento or held at an adhesion voltage V_(A) opposite in polarity from therepelling voltage V_(T) of the repelling surface 304. Referring to FIG.1, the voltage source 134 may apply such an attraction voltage to theadhesion surface 324. A charged particle 208 b proximate the adhesionsurface 324 may be intermittently or periodically attracted to orreceive a reduced repulsion from an adhesion voltage V_(A). For example,the adhesion voltage V_(A) may be at ground, may be opposite in sign(polarity) from the charged particle 208 b, or as described above, at areduced magnitude compared to the repelling voltage V_(T).

According to an embodiment, the adhesion voltage V_(A) may be modulatedin phase with a variation in passing charged particle 208 concentrationand/or sign. The phase may optionally be selected responsive to massflow rate, fuel burn rate, and/or flow velocity of the combustion gas207. According to another embodiment, the adhesion voltage V_(A) mayfollow a phase-delayed varying equilibrium with a concentration and/orsign of passing charged particles 208.

FIG. 4 illustrates an embodiment 401 from an A-A view illustrated onFIG. 3A including an adhesion surface 324 having a spanwise varyingadhesion surface coupling efficiency, charge/voltage, or area. Areas 402may be extended into or past regions of the adhesion surface 324. Theareas 402 may be an extension of the repelling surface 304, for example.A reduced repelling force and/or increased attracting (adhesion) forcefelt by a charge 208 a when proximate the adhesion surface 324 incombination with repelling force felt by a charge 208 may tend to causea spanwise acceleration variation that is conducive to formingstreamwise vortices 404. Streamwise vortices may tend to have desirableaerodynamic effects compared to spanwise vortices.

Various physical embodiments of the adhesion surface 324 arecontemplated. According to embodiments, the adhesion surface 324 may beconfigured to apply at least reduced Coulombic repulsion on thecombustion gas stream 207 compared to the repelling surface 304. Asillustrated in FIGS. 4-6, the adhesion surface 324 may include aspanwise variation in applied voltage, charge, or area configured topromote streamwise vortex 404 generation.

According to an embodiment, the adhesion surface 324 may be configuredto apply Coulombic attraction to the combustion gas stream 207. Forexample, a gas turbine 101 (FIG. 1) may include a voltage source 134operatively coupled to the adhesion surface 324 and configured toprovide an adhesion voltage to the adhesion surface 324. The turbineblade 302 may include an electrical lead (not shown) operatively coupledto the adhesion surface 324, the electrical lead being configured toconduct a voltage to at least a portion of the adhesion surface 324. Theelectrical lead may receive the adhesion voltage from the voltage source134.

The adhesion surface 324 may be shaped to occupy a void 406 defined bythe repelling surface 304. The adhesion surface 324 may include anelectrical insulator 408 adjacent to one or more voids 406 defined bythe repelling surface 304. An electrical conductor or semiconductor 410,operable as an adhesion electrode, may be disposed adjacent to theelectrical insulator 408. For example, the electrical conductor orsemiconductor (adhesion electrode) 410 may be disposed in a recess orvoid 412 defined by the electrically insulating material 408. A secondelectrical insulator or semiconductor portion 408 may be disposed overthe electrical conductor or semiconductor 410 forming the adhesionelectrode. In such an arrangement, the adhesion electrode 410 may bereferred to as “buried”. According to other embodiments, the adhesionelectrode 410 may be exposed.

The adhesion surface 324 may comprise at least a flow rearward portion330 of a low pressure side of the turbine blade 302. The repellingsurface 304 may include substantially the remainder of the surface ofthe turbine blade 302. According to embodiments, the repelling surface304 may include at least a flow forward portion of a low pressure sideof the turbine blade 302 and at least a portion of a high pressure sideof the turbine blade 302.

Referring to FIGS. 1 and 2, the voltage source 134 may be configured tocause modulation of at least one of a sign or concentration of chargedparticles 208 in the combustion gas stream 207. The voltage source 134may be configured to select the modulation to cause a selectedequilibrium voltage carried by the adhesion surface 324. The voltagesource may optionally be configured to apply a substantially constant ormodulated adhesion voltage to the adhesion surface 324 of the turbineblade 302.

Referring again to FIG. 4, the adhesion surface 324 may include a“buried” adhesion electrode 410, wherein the insulator 408 covers theconductor or semiconductor forming the adhesion electrode 410. Accordingto other embodiments, the adhesion electrode 410 may include an exposedupper surface (as shown in FIG. 3A).

According to embodiments, tantalum (Ta) may form at least a portion oralloy of the adhesion electrode 410. Tantalum may be advantageous due toits relatively high electrical opacity.

As described above, the adhesion surface 324 may include a spanwisevariation in area with regions having relatively high area and regionshaving relatively low area. According to other embodiments, the adhesionsurface 324 may be configured to support a spanwise variation in appliedvoltage or charge, or a spanwise variation in coupling efficiency to thecombustion gas 207.

Various arrangements are contemplated. FIG. 5 is a span-wise B-B view ofportions of a repelling surface 304 and an adhesion surface 324 of theturbine blade of FIGS. 3A and 4, according to an embodiment wherein theadhesion surface 324 has a spanwise variation in area. FIG. 6 is aspan-wise B-B view of a portion of the turbine blade of FIGS. 3A and 4according to another embodiment wherein the adhesion surface 324 has aspanwise variation in area. The spanwise variations in area depicted inFIGS. 5 and 6 may also help analogously describe the effect of aspanwise variation in voltage, charge, and/or coupling efficiency.

FIG. 5 illustrates an embodiment 501 wherein the area of the adhesionsurface 324 is varied spanwise by a serpentine variation in the positionof the adhesion surface 324 leading edge. A void may be machined in thesurface 304 of the turbine blade 302, and an insulator 408 appliedtherein. A void may then be machined in the insulator 408 surface and anadhesion electrode 410 disposed in the insulator void.

Streamlines superimposed over the adhesion surface indicate relativecombustion gas flow over the turbine blade surface. Streamwise vortices404 may be set up by a difference between repulsion of the chargedparticles 208 from the repelling surface 304 and the adhesion electrode410.

FIG. 6 illustrates an alternative embodiment wherein the leading edge ofthe adhesion electrode 410 is not varied, but wherein a plurality ofdiscontinuous regions of repelling surface 304 are arranged topotentiate the formation of streamwise vortices 404. According to otherembodiments (not shown), the adhesion surface and/or the adhesionelectrode 410 may include a plurality of discontinuous regions.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments are contemplated. The various aspects andembodiments disclosed herein are for purposes of illustration and arenot intended to be limiting, with the true scope and spirit beingindicated by the following claims.

1. A gas turbine, comprising: a combustor configured to output acombustion gas stream at least intermittently or periodically includingcharged particles having a first sign; and a turbine configured toreceive the combustion gas stream and including at least one turbinestage having turbine blades, each turbine blade of the at least onestage including: a repelling surface configured to be at leastintermittently or periodically held or driven to a repelling voltagehaving a polarity the same as the charged particles having the firstsign, an adhesion surface configured to be at least intermittently orperiodically held, driven, or in equilibrium to an adhesion voltage orcharge having lower magnitude than or opposite polarity from therepelling voltage, and an air channel configured to deliver film-coolingair adjacent to the repelling surface.
 2. (canceled)
 3. The gas turbineof claim 1, wherein the repelling surface is configured to repel thecombustion gas stream by Coulombic repulsion; and wherein thefilm-cooling air occupies a volume adjacent to the repelling surfacebetween the repelling surface and the combustion gas stream.
 4. The gasturbine of claim 1, wherein the adhesion surface is configured to applyat least reduced Coulombic repulsion on the combustion gas streamcompared to the repelling surface.
 5. The gas turbine of claim 1,wherein the adhesion surface is configured to apply Coulombic attractionto the combustion gas stream.
 6. The gas turbine of claim 1, wherein theadhesion surface includes a spanwise variation in applied voltage,charge, or area configured to promote streamwise vortex generation. 7.The gas turbine of claim 1, further comprising: a voltage sourceoperatively coupled to the adhesion surface and configured to providethe adhesion voltage to the adhesion surface.
 8. The gas turbine ofclaim 1, wherein the adhesion surface is configured as an electricalshield to shield the combustion gas stream from the repelling voltage.9. The gas turbine of claim 1, wherein the adhesion surface includes isshaped to occupy a void defined by the repelling surface.
 10. The gasturbine of claim 1, wherein the adhesion surface further comprises: anelectrical insulator adjacent to one or more voids defined by therepelling surface; and an electrical conductor or semiconductor adjacentto the electrical insulator.
 11. The gas turbine of claim 1, wherein theadhesion surface further comprises: in a recess or void defined by therepelling surface, an electrically insulating material; and in a recessor void defined by the electrically insulating material, an electricallyconductive or semiconductive adhesion electrode.
 12. The gas turbine ofclaim 11, wherein the electrically conductive or semiconductive adhesionelectrode is configured to be in charge equilibrium orpseudo-equilibrium with the charged combustion gas stream.
 13. The gasturbine of claim 12, wherein the electrically conductive orsemiconductive adhesion electrode is configured to be charged to anaverage voltage lower in magnitude than an average of the turbine bladerepelling voltage.
 14. The gas turbine of claim 12, wherein at least oneof the sign of the charged particles or the concentration of the chargedparticles is modulated according to a desired equilibrium orpseudo-equilibrium voltage.
 15. The gas turbine of claim 1, wherein theadhesion surface comprises at least a flow rearward portion of a lowpressure side of the turbine blade.
 16. The gas turbine of claim 15,wherein the repelling surface includes substantially the remainder ofthe surface of the turbine blade.
 17. The gas turbine of claim 1,wherein the repelling surface includes at least a flow forward portionof a low pressure side of the turbine blade and at least a portion of ahigh pressure side of the turbine blade.
 18. The gas turbine of claim 1,further comprising: a gas turbine controller, configured to causemodulation of at least one of a sign or concentration of chargedparticles in the combustion gas stream.
 19. The gas turbine of claim 18,wherein the gas turbine controller is configured to select themodulation to cause a selected equilibrium voltage carried by theadhesion surface.
 20. The gas turbine of claim 1, further comprising: agas turbine controller configured to apply a substantially constant ormodulated adhesion voltage to the adhesion surface of the turbine blade.21. The gas turbine of claim 1, wherein each turbine blade furthercomprises: a first air channel configured to deliver film-cooling airthrough slots or holes proximate a flow forward edge of the repellingsurface.
 22. The gas turbine of claim 21, wherein each turbine bladefurther comprises: a second air channel configured to deliver coolingair through slots or holes proximate the adhesion surface.
 23. The gasturbine of claim 22, wherein the adhesion surface includes a spanwisevariation in area with regions having relatively high area and regionshaving relatively low area; and wherein the slots or holes proximate theadhesion surface are aligned with or preferentially distributed near theregions having relatively low area and are configured to impart upwardmomentum on the combustion gas stream and on film-cooling air flowingover the slots or holes; whereby the slots or holes proximate theadhesion surface and the spanwise variation in area of the adhesionsurface are configured to cooperate to promote streamwise vortexgeneration.
 24. The gas turbine of claim 23, further comprising: acharge source configured to insert charged particles having the firstsign into the second air channel at least when the charged particleshaving the first sign in the combustion gas are proximate the turbineblade.
 25. The gas turbine of claim 22, wherein the adhesion surfaceincludes a spanwise variation in area include regions having relativelyhigh area and regions having relatively low area; and wherein the slotsor holes proximate the adhesion surface are aligned with orpreferentially distributed near the regions having relatively high area.26. The gas turbine of claim 25, further comprising: electricalinsulation to electrically isolate the second air channel from portionsof the turbine blade carrying the repelling voltage; and a charge sourceconfigured to insert charged particles having a second sign opposite inpolarity to the first sign into the second air channel at least when thecharged particles having the first sign in the combustion gas areproximate the turbine blade; whereby the charged particles having thesecond sign flowing through slots or holes proximate the adhesionsurface and the spanwise variation in area of the adhesion surface areconfigured to cooperate to promote streamwise vortex generation.
 27. Thegas turbine of claim 1, further comprising: an electrode locatedupstream of the turbine configured to be driven to a voltage sufficientto undergo corona discharge and at least intermittently or periodicallyadd charged particles having the first sign or a second sign differentthan the first sign to the combustion gas stream.
 28. The gas turbine ofclaim 1, wherein the combustor is configured to burn a fuel containingan additive to increase the production of the charged particles havingthe first sign.
 29. A method of operating a gas turbine, comprising:providing a combustion gas stream at least intermittently orperiodically carrying charged particles having a first sign; convertingthermodynamic energy to rotational energy with turbine blades; at leastintermittently or periodically applying Coulombic repulsion to thecharged particles from a repelling portion of each turbine blade byapplying a repelling voltage to the repelling portion; and at leastintermittently or periodically applying reduced Coulombic repulsion fromor increased Coulombic attraction to an adhesion portion of each turbineblade surface by at least one of shielding the Coulombic repulsioncaused by the repelling voltage or by applying an adhesion voltage tothe adhesion portion of the turbine blade surface.
 30. The method ofoperating a gas turbine of claim 29, further comprising: deliveringfilm-cooling gas adjacent to at least the repelling portion.
 31. Themethod of operating a gas turbine of claim 30, wherein the Coulombicrepulsion does not apply a force directly to the film-cooling gas. 32.The method of operating a gas turbine of claim 30, wherein thefilm-cooling gas is caused to preferentially stream adjacent to therepelling portion of the turbine blade responsive to the Coulombicrepulsion of the charged particles in the combustion gas stream.
 33. Themethod of operating a gas turbine of claim 29, wherein at leastintermittently or periodically applying reduced Coulombic repulsion fromor Coulombic attraction to the adhesion portion of each turbine bladesurface includes applying a spanwise variation in voltage of theadhesion portion.
 34. The method of operating a gas turbine of claim 29,wherein at least intermittently or periodically applying reducedCoulombic repulsion from or Coulombic attraction to an adhesion portionof each turbine blade surface includes applying a spanwise variation incharge carried by the adhesion surface.
 35. The method of operating agas turbine of claim 29, wherein the adhesion portion includes aspanwise variation in area; and wherein at least intermittently orperiodically applying reduced Coulombic repulsion from or Coulombicattraction to an adhesion portion of each turbine blade surface includesapplying a spanwise variation in repelling voltage responsive to thespanwise variation in adhesion area.
 36. The method of operating a gasturbine of claim 29, wherein at least intermittently or periodicallyapplying reduced Coulombic repulsion from or Coulombic attraction to anadhesion portion of each turbine blade surface includes at leastintermittently or periodically applying a spanwise varying reducedCoulombic repulsion from or Coulombic attraction to an adhesion portionof each turbine blade surface.
 37. The method of operating a gas turbineof claim 36, wherein the spanwise variation in reduced Coulombicrepulsion from or Coulombic attraction to the adhesion portion furthercooperates with an aerodynamic response of each turbine blade to causestreamwise vortices to form proximate a flow rearward portion of eachturbine blade.
 38. The method of operating a gas turbine of claim 37,wherein the streamwise vortices correspond to a spatially periodicspanwise increase in adhesion of the combustion gas to each turbineblade.
 39. The method of operating a gas turbine of claim 29, whereinproviding a combustion gas stream at least intermittently orperiodically carrying charged particles having a first sign includesmodulating charged particle concentration or charged particleconcentration and sign; and wherein applying a repelling voltage to therepelling portion of each turbine blade includes modulating therepelling voltage synchronously with the modulated charged particleconcentration or charged particle concentration and sign proximate eachturbine blade.
 40. The method of operating a gas turbine of claim 39,wherein at least intermittently or periodically applying reducedCoulombic repulsion from or a Coulombic attraction to the adhesionportion of the turbine blade surface includes maintaining atime-averaged equilibrium or pseudo-equilibrium with the modulatedcharged particle concentration or charged particle concentration andsign in the combustion gas.
 41. The method of operating a gas turbine ofclaim 39, wherein at least intermittently or periodically applyingreduced Coulombic repulsion from or a Coulombic attraction to theadhesion portion of the turbine blade surface includes holding theadhesion portion of the turbine blade surface at ground or modulatingthe adhesion portion of the turbine blade surface to one or morevoltages opposite in sign from the combustion gas charge proximate theturbine blade.
 42. The method of operating a gas turbine of claim 39,wherein at least intermittently or periodically applying reducedCoulombic repulsion from or a Coulombic attraction to the adhesionportion of the turbine blade surface includes modulating a voltagecarried by the adhesion portion of the turbine blade surface inverselywith a combustion gas charge concentration proximate the turbine blade.43. The method of operating a gas turbine of claim 29, wherein at leastintermittently or periodically applying Coulombic repulsion to thecharged particles from the repelling portion of the turbine bladesurface includes modulating the repelling portion of the turbine bladesurface to one or more voltages synchronously with a chargeconcentration or charge concentration and sign in the combustion gasproximate the turbine blade.
 44. The method of operating a gas turbineof claim 43, wherein the charged particles in the combustion gas streamproximate the turbine blade and the repelling voltage are the same sign;and wherein the repelling voltage is varied synchronously and inverselywith the charged particle concentration.
 45. The method of operating agas turbine of claim 43, wherein the charged particles in the combustiongas stream proximate the turbine blade and the repelling voltage areopposite signs; and wherein the repelling voltage is variedsynchronously with the charged particle concentration.
 46. The method ofoperating a gas turbine of claim 29, further comprising: deliveringfirst film-cooling gas through slots or holes proximate a flow forwardedge of the repelling portion.
 47. The method of operating a gas turbineof claim 29, further comprising: delivering second gas through slots orholes proximate the adhesion portion.
 48. The method of operating a gasturbine of claim 47, wherein the adhesion portion includes a spanwisevariation in area with regions having relatively high area and regionshaving relatively low area; wherein the slots or holes proximate theadhesion portion are aligned with or preferentially distributed near theregions having relatively low area; further comprising: imparting upwardmomentum on the combustion gas stream flowing over the slots or holesproximate the adhesion surface to cooperate with the spanwise variationin area of the adhesion portion to promote streamwise vortex generation.49. The method of operating a gas turbine of claim 48, furthercomprising: inserting charged particles having the first sign into thesecond gas at least when the charged particles having the first sign inthe combustion gas are proximate the turbine blade.
 50. The method ofoperating a gas turbine of claim 47, wherein the adhesion surfaceincludes a spanwise variation in area include regions having relativelyhigh area and regions having relatively low area; and wherein deliveringthe second gas includes delivering the second gas through the slots orholes proximate the adhesion portion that are aligned with orpreferentially distributed near the regions having relatively high area.51. The method of operating a gas turbine of claim 50, furthercomprising: inserting charged particles having a second sign opposite inpolarity from the first sign into the second gas at least when thecharged particles having the first sign in the combustion gas areproximate the turbine blade, the insertion of charged particlescooperating with the spanwise variation in area of the adhesion surfaceto promote streamwise vortex generation.
 52. The method for operating agas turbine of claim 29, further comprising: driving an electrodeupstream of the turbine blades to a sufficient voltage to achieve coronadischarge.
 53. The method for operating a gas turbine of claim 29,further comprising: combusting a fuel containing an additive to producethe combustion gas stream, the additive being selected to increase anumber density of the charged particles.
 54. A turbine blade,comprising: a repelling surface configured to be at least intermittentlyor periodically held or driven to a repelling voltage; and an adhesionsurface configured to be at least intermittently or periodically held,driven, or in equilibrium to an adhesion voltage or charge having lowermagnitude than or opposite polarity from the repelling voltage.
 55. Theturbine blade of claim 54, further comprising a gas channel configuredto deliver film-cooling gas adjacent to at least the repelling surface.56. The turbine blade of claim 55, wherein the repelling surface isconfigured to repel a combustion gas stream by Coulombic repulsion; andwherein the gas channel is configured to deliver the film-cooling gas toa volume adjacent to the repelling surface between the repelling surfaceand the combustion gas stream.
 57. The turbine blade of claim 54,wherein the adhesion surface further comprises: an electrical insulatordisposed adjacent to the repelling surface; and an electrical conductoror semiconductor disposed adjacent to the electrical insulator.
 58. Theturbine blade of claim 57, wherein the adhesion surface furthercomprises: a second electrical insulator or semiconductor disposed overthe electrical conductor or semiconductor.
 59. The turbine blade ofclaim 57, wherein the electrical conductor or semiconductor isconfigured to electrically shield a combustion gas stream from therepelling surface.
 60. The turbine blade of claim 57, wherein theelectrical conductor or semiconductor is configured to apply at leastreduced Coulombic repulsion to a combustion gas stream compared to therepelling surface.
 61. The turbine blade of claim 54 wherein theadhesion surface is configured to apply at least reduced Coulombicrepulsion on a combustion gas stream compared to the repelling surface.62. The turbine blade of claim 54, wherein the adhesion surface isconfigured to apply Coulombic attraction to a combustion gas stream. 63.The turbine blade of claim 54, wherein the adhesion surface isconfigured to support a spanwise variation in applied voltage or charge.64. The turbine blade of claim 54, wherein the adhesion surface includesa spanwise variation in area.
 65. The turbine blade of claim 54, furthercomprising: an electrical lead operatively coupled to the adhesionsurface, the electrical lead being configured to conduct a voltage to atleast a portion of the adhesion surface.
 66. The turbine blade of claim54, wherein the adhesion surface is shaped to occupy a void defined bythe repelling surface.
 67. The turbine blade of claim 54, wherein theadhesion surface further comprises: in a recess or void defined by therepelling surface, and electrically insulating material; and in a recessor void defined by the electrically insulating material, an electricallyconductive or semiconductive adhesion electrode.
 68. The turbine bladeof claim 67, wherein the electrically conductive or semiconductiveadhesion electrode is configured to be in charge equilibrium orpseudo-equilibrium with a charged combustion gas stream.
 69. The turbineblade of claim 68, wherein the electrically conductive or semiconductiveadhesion electrode is configured to be charged to an average voltagelower in magnitude than an average of a turbine blade repelling voltage.70. The turbine blade of claim 54, wherein the adhesion surfacecomprises at least a flow rearward portion of a low pressure side of theturbine blade.
 71. The turbine blade of claim 70, wherein the repellingsurface includes substantially the remainder of the surface of theturbine blade.
 72. The turbine blade of claim 54, wherein the repellingsurface includes at least a flow forward portion of a low pressure sideof the turbine blade and at least a portion of a high pressure side ofthe turbine blade.
 73. The turbine blade of claim 54, furthercomprising: a first gas channel configured to deliver film-cooling gasthrough slots or holes proximate a flow forward edge of the repellingsurface.
 74. The turbine blade of claim 73, further comprising: a secondgas channel configured to deliver cooling gas through slots or holesproximate the adhesion surface.
 75. The turbine blade of claim 74,wherein the adhesion surface includes a spanwise variation in area withregions having relatively high area and regions having relatively lowarea; and wherein the slots or holes proximate the adhesion surface arealigned with or preferentially distributed near the regions havingrelatively low area and are configured to impart upward momentum on acombustion gas stream and on film-cooling air flowing over the slots orholes.
 76. The turbine blade of claim 75, further comprising: a chargesource configured to at least intermittently or periodically insertcharged particles having a first sign into the second gas channel. 77.The turbine blade of claim 74, wherein the adhesion surface includes aspanwise variation in area include regions having relatively high areaand regions having relatively low area; and wherein the slots or holesproximate the adhesion surface are aligned with or preferentiallydistributed near the regions having relatively high area.
 78. Theturbine blade of claim 77, further comprising: electrical insulation toelectrically isolate the second air channel from portions of the turbineblade carrying the repelling voltage.
 79. The turbine blade of claim 78,further comprising: a charge source configured to insert chargedparticles having a second sign opposite in polarity from the repellingvoltage at least intermittently or periodically.
 80. The turbine bladeof claim 74, wherein the adhesion surface includes a plurality ofdiscontinuous regions.